Power cord for use with a leakage current detection and interruption device

ABSTRACT

A power supply cord for use with a leakage current detection and interruption device, including at least two power supply lines, at least two insulating layers respectively covering the at least two power supply lines, at least two shield lines respectively covering the at least two insulating layers, and at least one insulating structure covering at least one of the at least two shield lines to electrically insulate the at least two shield lines from each other. By providing the insulating structure outside of at least one of the shield lines, the shield lines of different power supply lines are independent of each other, so that the shield lines can better detect leakage currents in the power supply lines.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to electrical appliances, and in particular, itrelates to an intelligent leakage current detection and interruptiondevice for power cord.

Description of Related Art

Leakage current detection and interruption devices (LCDI) are a type ofsafety device to protect against electrical fire. Its main structure isa power cord with a power plug, and it functions to detect leakagecurrent between the hot line or neutral line and the shield layer alongthe cord from the plug to the electrical load (e.g., air conditioner,dehumidifier, etc.). When a leakage current is detected, the deviceinterrupts the electrical power to the load to prevent fire and ensuresafety. Such devices can prevent arc fault fire due to damaged andimproper insulation of the hot line, neutral line and ground line of thepower cord, which may be caused by aging, wear and tear, pinching,animal chewing, etc.

Current LCDI devices (see FIG. 1) has the following problems: when theleakage current detection line (shield line) 24 for the hot line L 21 orneutral line N 22 of the power line 2 is an open circuit and has lostits protection function, the power cord can still function to conductpower to the load. This presents a hidden threat of fire or other safetyissue.

Therefore, there is a need for a leakage current detection andinterruption device that can effectively detect leakage current.

SUMMARY

Accordingly, the present invention is directed to an intelligent leakagecurrent detection and interruption device for a power cord, whichincludes: a switch module, configured to control an electricalconnection of first and second power lines between their input andoutput ends; a leakage current detection module, including first andsecond leakage current detection lines coupled in series, configured todetect a leakage current on the first and second power lines,respectively; a detection monitoring module, coupled in series to thefirst and second leakage current detection lines and to the first andsecond power lines, configured to detect an open circuit condition inthe first or second leakage current detection line; and a drive module,coupled to the switch module, the leakage current detection module andthe detection monitoring module, configured to drive the switch moduleto cut off power to the output end in response to any detected leakagecurrent or open circuit condition.

In another aspect, the present invention provides a power supply cordfor use with a leakage current detection and interruption device, whichincludes: at least two power supply lines; at least two insulatinglayers respectively covering the at least two power supply lines; atleast two shield lines respectively covering the at least two insulatinglayers; and at least one insulating structure covering at least one ofthe at least two shield lines to electrically insulate the at least twoshield lines from each other.

The leakage current detection and interruption device can detect whetherthe first and second leakage current detection lines are intact with noopen circuit conditions, thereby enhancing the reliability of thedevice.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention are described withreference to the drawings. These drawings serve to explain theembodiments and their operating principle, and only illustratestructures that are necessary to the understanding of the principles ofthe invention. These drawings are not necessarily to scale. In thedrawings, like features are designated by like reference symbols.

FIG. 1 is a circuit diagram of a conventional LCDI device.

FIG. 2 is an exterior view of a power plug according to embodiments ofthe present invention.

FIG. 3 is a cross-sectional view of the cord.

FIG. 4A is a circuit diagram showing an LCDI device according to a firstembodiment of the present invention.

FIG. 4B is a circuit diagram showing an LCDI device according to asecond embodiment of the present invention.

FIG. 5A is a circuit diagram showing an LCDI device according to a thirdembodiment of the present invention.

FIG. 5B is a circuit diagram showing an LCDI device according to afourth embodiment of the present invention.

FIG. 6A is a circuit diagram showing an LCDI device according to a fifthembodiment of the present invention.

FIG. 6B is a circuit diagram showing an LCDI device according to a sixthembodiment of the present invention.

FIG. 7 is a circuit diagram showing an LCDI device according to aseventh embodiment of the present invention.

FIG. 8 is a circuit diagram showing an LCDI device according to aneighth embodiment of the present invention.

FIG. 9 is a circuit diagram showing an LCDI device according to a ninthembodiment of the present invention.

FIG. 10 is a circuit diagram showing an LCDI device according to a tenthembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below withreference to the drawings. These drawings and descriptions explainembodiments of the invention but do not limit the invention. Thedescribed embodiments are not all possible embodiments of the presentinvention. Other embodiments are possible without departing from thespirit and scope of the invention, and the structure and/or logic of theillustrated embodiments may be modified. Thus, it is intended that thescope of the invention is defined by the appended claims.

In the descriptions below, terms such as “including” are intended to beopen-ended and mean “including without limitation”, and can includeother contents. “Based on” means “at least partly based on.” “Anembodiment” means “at least one embodiment.” “Another embodiment” means“at least another embodiment,” etc.

Embodiments of the present invention provide an intelligent leakagecurrent detection and interruption device for a power cord, whichincludes: a switch module, configured to control an electricalconnection between a power input end and a power output end of a firstand a second power lines; leakage current detection module, including afirst leakage current detection line and a second leakage currentdetection line coupled in series, configured to detect whether a leakagecurrent is present on the first power line and the second power line,respectively; a detection monitoring module, coupled to the leakagecurrent detection module, by coupling in series to the first and secondleakage current detection lines, and configured to detect whether anopen circuit condition is present in the first or second leakage currentdetection line; and a drive module, including at least one semiconductordevice, wherein the drive module is coupled to the switch module, theleakage current detection module and the detection monitoring module,and is configured to drive the switch module to cut off power to thepower output end in response to the leakage current and the open circuitcondition.

As shown in FIG. 2, the intelligent leakage current detection andprotection device for a power cord has a plug 1 and an external powercord 2. The plug 1 includes a test switch TEST and a reset switch RESET.In the embodiment shown in FIG. 2, the power cord 2 includes a hot line(L) 21, a neutral line (N) 22, a ground line (G) 23, leakage currentdetection lines (shield lines) 241 and 242, and an insulating cover 27.The exterior cross-section of the power cord 2 may be round, where thehot line 21, neutral line 22, and ground line 23 are respectivelycovered by insulating layers 21A, 22A and 23A (see FIG. 3). In theembodiment shown in FIG. 3, the leakage current detection lines 241 and242 respectively cover (surround) the insulating layers 21A and 22A. Itshould be understood that the exterior cross-section of the power cord 2may be oblong with a side-by-side configuration, or other shapes. Itshould also be understood that in other embodiments, the power cord 2may include other signal lines. As shown in FIG. 3, the power cord 2 mayinclude filling materials 26. The leakage current detection line 241 iscovered by an insulating structure 28, but the leakage current detectionline 242 is not covered by such an insulating structure. Alternatively(not shown), leakage current detection line 242 is covered by aninsulating structure, but the leakage current detection line 241 is notcovered by such an insulating structure. Or (not shown), both leakagecurrent detection lines 241 and 242 are separately covered by aninsulating structure. The leakage current detection lines 241 and 242may be woven structures made of metal (e.g., copper, aluminum, etc.)(see FIG. 3), or a wound structures formed of one or more metal wires(not shown in the drawings), or metal foil covers (not shown in thedrawings), or combinations of the above. The insulating structure 28 maybe a plastic material formed in one piece, or it may be formed ofinsulating paper or fabric or other insulating materials surrounding thewires. The leakage current detection lines 241 and 242 may be aone-sided insulating material (i.e., a sheet material that iselectrically conductive on one side and electrically insulating on theopposite side) forming a cover, which can eliminate the need for aseparate insulating structure 28 (not shown in the figures). The leakagecurrent detection line 241 encloses at least one power supply wire(e.g., current carrying lines like the hot line (L) 21, the neutral line(N) 22, etc.). The leakage current detection line 241 may simultaneouslyencloses both the hot line 21 and the neutral line 22, the insulatingstructure 28 encloses the leakage current detection line 241 and theground line 23, and the leakage current detection line 242 encloses theinsulating structure 28. It should be understood that the leakagecurrent detection line 241 or the leakage current detection line 242 maysimultaneously encloses multiple power supply wires (current carryingwires).

FIG. 4A is a circuit diagram showing an LCDI device according to a firstembodiment of the present invention. As shown in FIG. 4A, theintelligent leakage current detection and interruption device 100 for apower cord includes a switch module 141, a leakage current detectionmodule 142, a detection monitoring module 143, and a drive module 144.The switch module 141 includes a reset switch RESET. The switch module141 is configured to control the electrical connection between a powerinput end LINE and a power output end LOAD of the device. The leakagecurrent detection module 142 includes at least leakage current detectionlines 241 and 242. The leakage current detection lines 241 and 242 arecoupled in series via the load-side end C of the leakage currentdetection line 241 and the load-side end D of leakage current detectionline 242, and respectively function to detect whether a leakage currentis present on the hot line L and neutral line N. The detectionmonitoring module 143 is configured to detect whether the leakagecurrent detection lines 241 and 242 have any open circuit faultcondition. The detection monitoring module 143 includes diodes D4A andD4B, and resistors R6A and R6B. The anode of diode D4A is coupled inseries with one end of resistor R6A, and the cathode of diode D4A iscoupled to the hot line L and further to the reset switch RESET via thehot line L. The other end of resistor R6A is coupled to the line-sideend B of the leakage current detection line 241. The cathode of diodeD4B is coupled in series with one end of resistor R6B. The other end ofresistor R6B is coupled to the line-side end A of the leakage currentdetection line 242 and also to one end of another resistor R2. The anodeof diode D4B is coupled to the anode of a silicon controlled rectifierSCR of the drive module 144, and to one end of a solenoid SOL. The otherend of the solenoid SOL is coupled to the neutral line N. The solenoidSOL is mechanically coupled to the reset switch RESET of the switchmodule 141. The drive module 144 further includes diodes D1 and D2,capacitor C1, and resistors R2 and R3. The cathode and the control gateof the silicon controlled rectifier SCR are respectively coupled to thetwo ends of capacitor C1. Capacitor C1 is coupled in parallel withresistor R3. One end of resistor R2 is coupled to point A; the other endof resistor R2 is coupled to one end of the parallelly coupled capacitorC1 and resistor R3 and also to the control gate of the siliconcontrolled rectifier SCR. The anode of diode D1 is coupled to thecathode of the silicon controlled rectifier SCR. The cathode of diode D1is coupled to the hot line L and further to the switch module 141 viathe hot line L.

The working principle of the circuit of FIG. 4A is described below. Whenthe leakage current detection lines 241 and 242 are functioning normally(i.e., they do not have any open circuit condition), by the setting ofresistors R6A and R6B, the point A is limited to a relatively lowvoltage level, so the silicon controlled rectifier SCR is not triggeredto conduct. In this condition, when the LCDI device is connected to thepower source, it will function normally to conduct power to the load.When an open circuit condition exists at any point on the leakagecurrent detection line 241 and/or 242, a current loop is formed from theneutral line N via SOL-D4B-R6B-R2-R3-D1 to the hot line L, so that thevoltage across resistor R3 increases to a sufficient level to triggerthe silicon controlled rectifier SCR to be conductive. This forms acurrent loop from the neutral line N via SOL-SCR-D1 to the hot line L.As a result, the solenoid SOL generates a magnetic field to actuate thereset switch RESET, causing the device to trip and cut off power to theload.

As shown in FIG. 4A, the leakage current detection and interruptiondevice 100 further includes a test module 145, which includes resistorR4 and test switch TEST. One end of resistor R4 is coupled in series toone end of the test switch TEST; the other end of resistor R4 is coupledto the hot line L and further to the switch module 141 via the hot lineL. The other end of the test switch TEST is coupled between resistor R6Aand the leakage current detection line 241. Normally, the test switchTEST is open; so when the leakage current detection lines 241 and 242are functioning normally (no open circuit condition) and there is noleakage current between the power lines 21, 22, 23 and the leakagecurrent detection lines 241, 242, the silicon controlled rectifier SCRis not triggered and the LCDI device functions normally to conduct powerto the load. When the test switch TEST is closed (e.g., when manuallydepressed by a user), a simulated leakage current flows in a testcurrent loop from the hot line L via resistor R4, test switch TEST,leakage current detection lines 241 and 242, resistors R2 and R3, diodeD2, solenoid SOL to the neutral line N. This simulated current causesthe voltage across resistor R3 to increase to a sufficient level, whichtriggers the silicon controlled rectifier SCR to be conductive. As seenfrom FIG. 4A, when the silicon controlled rectifier SCR is conductive, atrip current loop is formed from the neutral line N via solenoid SOL,silicon controlled rectifier SCR, and diode D1 to the hot line L. As aresult, the current in the solenoid SOL generates a magnetic field toactuate the reset switch RESET, causing the device to trip and cut offthe power to the load. When any circuit or components on the testcurrent loop has an open circuit condition, the device will not tripwhen the test switch TEST is closed. Therefore, the user can manuallyoperate the test switch TEST to test whether the leakage currentdetection lines 241 and 242 are intact and functioning normally. Itshould be understood that the test switch TEST can test whether anycomponent on the test current loop has an open circuit condition. Itshould also be noted that when a true leakage current is present betweenthe hot line L and the leakage current detection line 241 or between theneutral line N and the leakage current detection line 242, such aleakage current will cause the solenoid SOL to actuate the reset switchbased on the same principle described above.

FIG. 4B is a circuit diagram schematically illustrating an LCDI deviceaccording to a second embodiment of the present invention. Thisembodiment is similar to the first embodiment in FIG. 4A, but here, thedetection monitoring module 143 does not include diodes D4A and D4B.Rather, the detection monitoring module 143 includes resistors R6A, R6Band diode D1. One end of resistor R6A is coupled to the point B of theleakage current detection line 241, and the other end of resistor R6A iscoupled to the cathode of the silicon controlled rectifier SCR. ResistorR6B is coupled between the anode of the silicon controlled rectifier SCRand the point A of the leakage current detection line 242. Diode D1 isshared by the drive module 144 and the detection monitoring module 143.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R6A and R6B, thepoint A is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered to conduct. In this condition,when the LCDI device is connected to the power source, it will functionnormally to conduct power to the load. When an open circuit conditionexists at any point on the leakage current detection line 241 and/or242, a current loop is formed from the neutral line N viaSOL-R6B-R2-R3-D1 to the hot line L, so that the voltage across resistorR3 increases to a sufficient level to trigger the silicon controlledrectifier SCR to be conductive. This forms a current loop from theneutral line N via SOL-SCR-D1 to the hot line L. As a result, thesolenoid SOL generates a magnetic field to actuate the reset switchRESET, causing the device to trip and cut off power to the load.

In this embodiment, the working principle of the test module 145 is thesame as in the first embodiment and will not be further described.

FIG. 5A is a circuit diagram schematically illustrating an LCDI deviceaccording to a third embodiment of the present invention. Thisembodiment is similar to the first embodiment in FIG. 4A, but here, thedetection monitoring module 143 does not include diode D4B. Rather, thedetection monitoring module 143 includes diode D4A and resistors R6A,R6B. One end of resistor R6B is coupled directly to the neutral line N,and further coupled to the switch module 141 via the neutral line N. Theother end of resistor R6B is coupled to point A of the leakage currentdetection line 242.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R6A and R6B, thepoint A is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load. When an open circuit condition exists atany point on the leakage current detection line 241 and/or 242, acurrent loop is formed from the neutral line N via R6B-R2-R3-D1 to thehot line L, so that the voltage across resistor R3 increases to asufficient level to trigger the silicon controlled rectifier SCR to beconductive. This forms a current loop from the neutral line N viaSOL-SCR-D1 to the hot line L. As a result, the solenoid SOL generates amagnetic field to actuate the reset switch RESET, causing the device totrip and cut off power to the load.

In this embodiment, the working principle of the test module 145 is thesame as in the first embodiment and will not be further described.

FIG. 5B is a circuit diagram schematically illustrating an LCDI deviceaccording to a fourth embodiment of the present invention. In thisembodiment, the detection monitoring module 143 has the same componentsas the second embodiment in FIG. 4B, but here, resistor R6B is connecteddifferently. In FIG. 5B, one end of resistor R6B is coupled directly tothe neutral line N without going through the solenoid SOL, and furthercoupled to the switch module 141 via the neutral line N. The other endof resistor R6B is coupled to point A of the leakage current detectionline 242.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R6A and R6B, thepoint A is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load. When an open circuit condition exists atany point on the leakage current detection line 241 and/or 242, acurrent loop is formed from the neutral line N via R6B-R2-R3-D1 to thehot line L, so that the voltage across resistor R3 increases to asufficient level to trigger the silicon controlled rectifier SCR to beconductive. This forms a current loop from the neutral line N viaSOL-SCR-D1 to the hot line L. As a result, the solenoid SOL generates amagnetic field to actuate the reset switch RESET, causing the device totrip and cut off power to the load.

In this embodiment, the working principle of the test module 145 is thesame as in the first embodiment and will not be further described.

FIG. 6A is a circuit diagram schematically illustrating an LCDI deviceaccording to a fifth embodiment of the present invention. Thisembodiment is similar to the first embodiment in FIG. 4A, but here, thedetection monitoring module 143 does not include diode D4A. Rather, thedetection monitoring module 143 includes resistor R6A, diode D4B andresistor R6B. One end of resistor R6A is coupled to the neutral line Nand further coupled to the switch module 141 via the neutral line N. Theother end of resistor R6A is coupled to the point B of the leakagecurrent detection line 242. The anode of diode D4B is coupled directlyto the hot line L without going through the solenoid SOL, and furthercoupled to the switch module 141 via the hot line L. The cathode ofdiode D4B is coupled to one end of resistor R6B, and the other end ofresistor R6B is coupled to the point A of the leakage current detectionline 242.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R6A and R6B, thepoint A is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load. When an open circuit condition exists atany point on the leakage current detection line 241 and/or 242, acurrent loop is formed from the hot line L via D4B-R6B-R2-R3-D2-SOL tothe neutral line N, so that the voltage across resistor R3 increases toa sufficient level to trigger the silicon controlled rectifier SCR to beconductive. This forms a current loop from the neutral line N viaSOL-SCR-D1 to the hot line L. As a result, the solenoid SOL generates amagnetic field to actuate the reset switch RESET, causing the device totrip and cut off power to the load.

In this embodiment, the working principle of the test module 145 is thesame as in the first embodiment except that resistor R4 is coupled tothe neutral line N and that the current flow direction of the testcurrent loop is from the neutral line N to the hot line L. Furtherdescriptions are omitted.

FIG. 6B is a circuit diagram schematically illustrating an LCDI deviceaccording to a sixth embodiment of the present invention. Thisembodiment is similar to the fifth embodiment in FIG. 6A, but here, thedetection monitoring module 143 does not include diode D4B. Rather, thedetection monitoring module 143 includes resistors R6A, R6B and diodeD2. One end (namely, the end on the left in the configuration of FIG.6B) of resistor R6A is not coupled to the neutral line N but rather,coupled to the cathode of the silicon controlled rectifier SCR. Diode D2is shared by the drive module 144 and detection monitoring module 143.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R6A and R6B, thepoint A is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load. When an open circuit condition exists atany point on the leakage current detection line 241 and/or 242, acurrent loop is formed from the hot line L via R6B-R2-R3-D2-SOL to theneutral line N, so that the voltage across resistor R3 increases to asufficient level to trigger the silicon controlled rectifier SCR to beconductive. This forms a current loop from the neutral line N viaSOL-SCR-D1 to the hot line L. As a result, the solenoid SOL generates amagnetic field to actuate the reset switch RESET, causing the device totrip and cut off power to the load. In this embodiment, the workingprinciple of the test module 145 is the same as in the fifth embodimentof FIG. 6A, and will not be further described.

FIG. 7 is a circuit diagram schematically illustrating an LCDI deviceaccording to a seventh embodiment of the present invention. Thisembodiment is similar to the third embodiment in FIG. 5A, but here, thedetection monitoring module 143 does not include diode D4A. Rather, thedetection monitoring module 143 includes resistor R6A, R6B and diode D4.Diode D4 is coupled between the point A of the leakage current detectionline 242 and resistor R2. The function of diode D4 is to preventdischarge of the energy stored in capacitor C1 during a half cycle ofthe AC current which would have caused capacitor C1 to be unable totrigger the silicon controlled rectifier SCR.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R6A and R6B, thepoint A is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load. When an open circuit condition exists atany point on the leakage current detection line 241 and/or 242, acurrent loop is formed from the neutral line N via R6B-D4-R2-R3-D1 tothe hot line L, so that the voltage across resistor R3 increases to asufficient level to trigger the silicon controlled rectifier SCR to beconductive. This forms a current loop from the neutral line N viaSOL-SCR-D1 to the hot line L. As a result, the solenoid SOL generates amagnetic field to actuate the reset switch RESET, causing the device totrip and cut off power to the load.

In this embodiment, the working principle of the test module 145 is thesame as in the third embodiment of FIG. 5A, and will not be furtherdescribed.

FIG. 8 is a circuit diagram schematically illustrating an LCDI deviceaccording to an eighth embodiment of the present invention. Thisembodiment is similar to the seventh embodiment in FIG. 7, but here,diode D4 is connected differently. In FIG. 8, diode D4 is shared by thedetection monitoring module 143 and the drive module 144. The cathode ofdiode D4 is coupled to the control gate of the silicon controlledrectifier SCR, and the anode of diode D4 is coupled between resistors R2and R3. The function of diode D4 is the same as in the seventhembodiment of FIG. 7.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R6A and R6B, thepoint A is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load. When an open circuit condition exists atany point on the leakage current detection line 241 and/or 242, acurrent loop is formed from the neutral line N via R6B-R2-R3-D1 to thehot line L, so that the voltage across resistor R3 increases to asufficient level to trigger the silicon controlled rectifier SCR to beconductive. This forms a current loop from the neutral line N viaSOL-SCR-D1 to the hot line L. As a result, the solenoid SOL generates amagnetic field to actuate the reset switch RESET, causing the device totrip and cut off power to the load.

In this embodiment, the working principle of the test module 145 is thesame as in the seventh embodiment of FIG. 7, and will not be furtherdescribed.

FIG. 9 is a circuit diagram schematically illustrating an LCDI deviceaccording to a ninth embodiment of the present invention. Thisembodiment is similar to earlier described embodiments, but here, thedetection monitoring module 143 includes a full-wave bridge rectifierand resistors R1 and R4. The full-wave bridge rectifier is shared by thedetection monitoring module 143 and drive module 144. The upper end(first end) of the full-wave bridge rectifier is coupled to the hot lineL, the right end (second end) of the full-wave bridge rectifier iscoupled to the anode of the silicon controlled rectifier SCR, the lowerend (third end) of the full-wave bridge rectifier is coupled via thesolenoid SOL to the neutral line N, and the left end (fourth end) of thefull-wave bridge rectifier is coupled to the cathode of the siliconcontrolled rectifier SCR. Resistor R1 is coupled between the anode ofthe silicon controlled rectifier SCR and the point B of the leakagecurrent detection line 241. Resistor R4 is coupled between the cathodeof the silicon controlled rectifier SCR and the point A of the leakagecurrent detection line 242.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R1 and R4, thepoint B is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load. When an open circuit condition exists atany point on the leakage current detection line 241 and/or 242, acurrent loop is formed from the hot line L via D1-R1-R2-R3-D3-SOL to theneutral line N, so that the voltage across resistor R3 increases to asufficient level to trigger the silicon controlled rectifier SCR to beconductive. This forms a current loop from the neutral line N viaSOL-D4-SCR-D2 to the hot line L. As a result, the solenoid SOL generatesa magnetic field to actuate the reset switch RESET, causing the deviceto trip and cut off power to the load.

In this embodiment, the working principle of the test module 145 issimilar to the earlier described embodiments with the followingdifferences. The test module 145 only includes the test switch TEST. Thetest switch TEST is coupled to the point A of the leakage currentdetection line 242. The test switch TEST is normally open; so when theleakage current detection lines 241 and 242 are functioning normally (noopen circuit condition) and there is no leakage current between thepower lines 21, 22, 23 and the leakage current detection lines 241, 242,the silicon controlled rectifier SCR is not triggered and the LCDIdevice functions normally to conduct power to the load. When the testswitch TEST is closed, a simulated leakage current flows in a testcurrent loop from the hot line L via test switch TEST, leakage currentdetection lines 241 and 242, resistors R2 and R3, diode D3, solenoid SOLto the neutral line N. This simulated current causes the voltage acrossresistor R3 to increase to a sufficient level, which triggers thesilicon controlled rectifier SCR to be conductive. As a result, thereset switch RESET is actuated to cut off power to the load.

FIG. 10 is a circuit diagram schematically illustrating an LCDI deviceaccording to a tenth embodiment of the present invention. Thisembodiment is similar to the ninth embodiments in FIG. 9, but here, theupper end of the full-wave bridge rectifier is coupled to the neutralline N, the lower end of the full-wave bridge rectifier is coupled viathe SOL to the hot line L, and the test switch TEST is coupled to thepoint B of leakage current detection line 241.

When the leakage current detection lines 241 and 242 are functioningnormally (no open circuit), by the setting of resistors R1 and R4, thepoint B is limited to a relatively low voltage level, so the siliconcontrolled rectifier SCR is not triggered. In this condition, when theLCDI device is connected to the power source, it will function normallyto conduct power to the load. When an open circuit condition exists atany point on the leakage current detection line 241 and/or 242, acurrent loop is formed from the neutral line N via D1-R1-R2-R3-D3-SOL tothe hot line L, so that the voltage across resistor R3 increases to asufficient level to trigger the silicon controlled rectifier SCR to beconductive. This forms a current loop from the hot line L viaSOL-D4-SCR-D2 to the neutral line N. As a result, the solenoid SOLgenerates a magnetic field to actuate the reset switch RESET, causingthe device to trip and cut off power to the load.

In this embodiment, the working principle of the test module 145 is thesame as in the ninth embodiment of FIG. 9, and will not be furtherdescribed.

In the above embodiments, one silicon controlled rectifier SCR is shown,but in other alternative embodiments, the circuit may includeparallel-coupled multiple silicon controlled rectifiers. Further, thesilicon controlled rectifier SCR may be replaced by MOS transistors,other transistors, or other semiconductor devices having controllablecurrent conducting functions.

The LCDI devices according to embodiments of the present invention cancut off power to the load when the leakage current detection lines havean open circuit condition, thereby improving the safety of the device.

While the present invention is described above using specific examples,these examples are only illustrative and do not limit the scope of theinvention. It will be apparent to those skilled in the art that variousmodifications, additions and deletions can be made to the LCDI device ofthe present invention without departing from the spirit or scope of theinvention.

What is claimed is:
 1. A power supply cord for use with a leakagecurrent detection and interruption device, comprising: at least twopower supply lines; at least two insulating layers respectively coveringthe at least two power supply lines; at least two leakage currentdetection lines respectively disposed around the at least two insulatinglayers, wherein the at least two leakage current detection lines includea first leakage current detection line and a second leakage currentdetection line each having a first end and a second end, wherein thesecond end of the first leakage current detection line is electricallycoupled to the second end or the second leakage current detection line,and the first and second leakage current detection lines are coupled inseries to form a current path from the first end of the first leakagecurrent detection line to the second end of the first leakage currentdetection line to the second end of the second leakage current detectionline to the first end of the second leakage current detection line; andat least one insulating structure covering at least one of the at leasttwo leakage current detection lines to electrically insulate the atleast two leakage current detection lines from each other.
 2. The powersupply cord of claim 1, wherein the at least one insulating structureand the corresponding at least one of the at least two leakage currentdetection lines are formed of a one-sided insulating material, which isa sheet material that is electrically conductive on one side andelectrically insulating on an opposite side.
 3. The power supply cord ofclaim 1, wherein the at least two leakage current detection lines areformed of woven structures made of a conductive material.
 4. The powersupply cord of claim 1, wherein the at least two leakage currentdetection lines are formed of metal foil covers.
 5. The power supplycord of claim 1, wherein the at least two leakage current detectionlines are wound structures formed of one or more metal wires.
 6. Thepower supply cord of claim 1, wherein the at least one insulatingstructure is made of a plastic material formed in one piece.
 7. Thepower supply cord of claim 1, wherein the at least one insulatingstructure is formed of insulating paper or fabric surrounding the atleast one of the at least two leakage current detection lines.
 8. Thepower supply cord of claim 1, comprising at least two insulatingstructures respectively covering the at least two leakage currentdetection lines.
 9. A leakage current detection and interruption devicecomprising the power supply cord of claim 1, further comprising: aswitch module, configured to control an electrical connection between apower source and the at least two power supply lines; a leakage currentdetection module, including the first and second leakage currentdetection lines that are coupled in series; and a switch drive module,coupled to the switch module and the leakage current detection module,configured to control the switch unit based on a leakage current signalgenerated by the leakage current detection module to disconnect theelectrical connection.
 10. The leakage current detection andinterruption device of claim 9, further comprising a testing unit, thetesting unit including a test switch coupled to the leakage currentprotection unit, wherein at least the test switch and the leakagecurrent protection unit form a test circuit, wherein when the testswitch is closed and the leakage current detection module is in a firststate, the switch drive module drives the switch unit to disconnect theelectrical connection.
 11. The leakage current detection andinterruption device of claim 10, wherein when the test switch is closedand the leakage current detection module is in a second state, theswitch unit maintains the electrical connection.